USPS Priority Mail vs. USPS Flat Rates: Which Is Best for eCommerce Shipping?

Flat rate shipping remains a popular shipping strategy in eCommerce as it’s very straightforward – charge one price regardless of the shipment weight. Since it’s so easy to understand, it’s common for eCommerce stores to use it as an alternative shipping promotion (after free shipping, of course).

Despite its popularity, flat rates have a bad rap for causing businesses to overspend on shipping. But as the adage says, “Everything in moderation.” There are situations when flat rates are the most cost-effective option; you just need to know when that is.

Many couriers offer flat rate shipping options, but we’ll focus on the United States Postal Service's ones for this post. We’ll discuss the break-even points for USPS flat rate shipping solutions, and how you can use a platform like Easyship to easily determine when flat rates are the best option to use.

Understanding USPS Zones

It’s useful to understand how USPS shipping zones work before diving into the break-even point analysis.

The postage rates for the following USPS domestic services are calculated by the weight of your mail/parcel and the distance it will travel:

• Priority Mail Express
• Priority Mail
• First-Class Package Service - Retail
• USPS Retail Ground

USPS has a zone chart to calculate the distance between the origin and destination zip codes. There are a total of 9 USPS zones, with Zones 1-8 covering the continental US, Alaska, Hawaii, and US Territories such as Puerto Rico and the Virgin Islands. Zone 9 zip codes include US Territories, Commonwealths, and the Freely Associated States that are mostly based in the Pacific Ocean, such as Guam, Northern Mariana Islands, and the Republic of the Marshall Islands, to name a few places.

Zone 1 contains zip codes that are nearest to the origin zip code. The larger the zone number, the further the destination zip code is – so Zone 9 zip codes are the furthest distance from the origin zip code.

Here's an example of what the USPS Zone Map would look like for a zip code in Los Angeles:

As you can see, the area near Los Angeles is purple, or Zone 1. All of the eastern United States, most of Alaska, and Hawaii are orange, or Zone 8, which shows they are the furthest from LA.

USPS zones are dynamic, meaning they will be different based on your location. Zone 1 for a Miami zip code would not be the same as Zone 1 for a Los Angeles zip code.

If you're curious about what zone you're shipping to, you can enter origin and destination zip codes when you visit USPS' Domestic Zone Chart.

USPS Priority Mail vs. USPS Small Flat Rate Box

Let’s start our break-even analysis by looking at the retail postage rates table for Priority Mail, and comparing it to the Small Flat Rate Box, priced at $7.90. Dimensions are 8 11/16" x 5 7/16" x 1 3/4".

USPS Priority Mail - Retail Pricing, 2019

Keep in mind that the first column is for weight not over a certain number of pounds. If your parcel weighs exactly 1 pound (1 lb, 0 oz), it will cost $7.35 to ship to Zone 1 & 2. However, if your parcel weighs 1 lb, 1 oz, that means it is over the 1 pound mark and it will instead cost $7.85 to ship to Zone 1 & 2.

When to use the USPS Small Flat Rate Box

According to the chart, if the shipment weighs 2 lbs, 1 oz, or heavier, the Priority Mail pricing will start at $8.30 for Zone 1 & 2. Since the Small Flat Rate Box rate is $7.90, it makes sense to use this flat-rate option to ship anything over 2 lbs.

However, if the shipment weighs under 2 lbs, it’s more economical to use the Small Flat Rate Box under the following circumstances:

USPS Small Flat Rate Box Exceptions: Under 2 Lbs

USPS Priority Mail vs. USPS Medium Flat Rate Box

The USPS Medium Flat Rate Box costs $14.35 and the outside dimensions are 14” x 12” x 3 ½”. Looking at the USPS pricing chart, we can see that if your shipment weighs under 2 pounds, USPS Priority Mail rates will be cheaper than the Medium Flat Rate Box. The only exception is if you are shipping something between 1 lb, 1 oz - 2 lbs to Zone 9; in this case, it’s best to use the Medium Flat Rate Box.

When to use the USPS Medium Flat Rate Box

According to the chart, if the shipment weighs 11 lbs, 1 oz, or heavier, the Priority Mail pricing will start at $15.20 for Zone 1 & 2. Since the Medium Flat Rate Box rate is $14.35, it makes sense to use this flat-rate option to ship anything over 11 lbs.

However, if the shipment weighs under 11 lbs, it’s more economical to use the Medium Flat Rate Box under the following circumstances:

USPS Medium Flat Rate Box Exceptions: Under 11 Lbs

USPS Priority Mail vs. USPS Large Flat Rate Box

The USPS Large Flat Rate Box costs $19.95, and the outside dimensions are 12 ¼” x 12 ¼” x 6”.

When to use the USPS Large Flat Rate Box

According to the pricing chart, if the shipment weighs 18 lbs, 1 oz, or heavier, the Priority Mail pricing will start at $20.05 for Zone 1 & 2. Since the Large Flat Rate Box rate is $19.95, it makes sense to use this flat-rate option to ship anything over 18 lbs.

However, if the shipment weighs under 18 lbs, it’s more economical to use the Large Flat Rate Box under the following circumstances:

USPS Large Flat Rate Box Exceptions: Under 18 Lbs

How To Avoid Overspending When Using USPS Flat Rate Shipping

While it’s nice to have a cheat sheet on all the break-even points in USPS Flat Rate Shipping, the multiple variables involved can make it hard to keep track of.

How can you efficiently ensure that flat rates apply to qualified shipments as they are being processed?

Using a platform like Easyship can help!

We currently offer the following flat rate solutions at commercial base pricing, which means you’ll be paying lower rates:

• Medium Flat Rate Box - 2 - $12.80
• Large Flat Rate Box - $17.60
• Padded Flat Rate Envelope - $7.55

Medium Flat Rate Box Comparison Pricing With Easyship

Here's an example of sending a 21-pound shipment within Zone 1. In this case, the origin is New York City and the destination is Syosset, Long Island, NY.

Assuming this shipment fits snugly in the medium flat rate box, you’ll notice that the flat rate option would be the most economical at $12.80 vs Priority Mail at $15.71. (Note: These rates are commercial base prices.)

Large Flat Rate Box Comparison Pricing With Easyship

Here’s an example of sending a 7-pound shipment to Zone 5. This example is from Atlanta to Houston.

Remember how we discovered it’s best to use the large flat rate box to ship anything over 18 lbs? In this case, the Easyship algorithm was able to show that shipping something that weighs 7 lbs to Zone 5 will be cheaper using Priority Mail at $10.34 vs the large flat rate box price of $17.60.

Conclusion

Looking at rates tables and trying to figure out at what weight and distance you would break even for each shipment all to save a few dollars isn’t a scalable solution. Instead, automate this task by syncing your orders on Easyship, and let our algorithm do the heavy lifting.

Our dashboard will provide complete visibility by including other available shipping solutions, making price comparisons a lot easier – fully eliminating the guesswork of whether flat rates will save you money or not.

Even better, we offer flat rates at commercial base pricing, which means you have immediate access to lower rates without having to negotiate with USPS on your own!

To start using USPS flat rates on Easyship, visit our Support Center article. No account yet? Sign up today!

USPS Priority Mail vs. USPS Flat Rates FAQ

Which is faster, flat rate, or standard shipping?

USPS Flat Rate generally takes between 1-3 business days, while other standard shipping services take anywhere from 3-4 business days.

Is USPS flat rate shipping the best way to ship 2-5lb items?

The small Flat Rate Box rate is $7.90, so it makes sense to use this flat-rate option to ship anything over 2 lbs.

Is flat rate shipping expensive?

No, flat rate shipping is an affordable shipping method for eCommerce businesses.